The present invention relates to a copier, printer facsimile apparatus or similar image forming apparatus and more particularly to a duplex image recording apparatus capable of forming images on both sides of a recording medium by a so-called interleaf control system.
In parallel with the spread of digital copiers, printers, facsimile apparatuses and other image forming apparatuses, there is an increasing demand for high productivity in relation to duplex copies. A current trend with a digital duplex image recording apparatus is toward an interleaf control system capable of promoting efficient printing. Japanese Patent Laid-Open Publication No. 63-313172, for example, teaches an interleaf control system that prints an image on the first side of the first paper sheet or similar recording medium, prints an image on the first side of the second or new paper sheet before returning the first paper sheet to a recording position, records an image on the second side of the first paper sheet, and repeats such alternate image formation thereafter.
It is a common practice with, e.g., a digital copier to read documents that are sequentially fed by an ADF (Automatic Document Feeder) mounted on the copier. The resulting image data are sequentially printed out in the order in which they are read or are written to, e.g., a memory so as to be printed out later, as needed.
The flow of paper sheets to occur in a duplex copy mode available with a conventional digital copier will be briefly described hereinafter. To produce a duplex copy, the copier prints an image on the first side or front of a paper sheet, reverses or turns back the paper sheet carrying the image on one side thereof, and returns the paper sheet to a recording position so as to form an image on the rear or second side of the paper sheet. Today, a stackless type of duplex recording system, which does not stack paper sheets in a duplex copy unit, is becoming predominant over the other duplex recording systems. The simplest duplex copying method is forming an image on the front of a paper sheet and then forms an image on the rear of the same paper sheet when the paper sheet is returned to a recording position. This method, however, lacks in efficiency and lowers productivity as the length of a duplex conveying path increases.
Specifically, assume that images are sequentially formed on the front of the first paper sheet, the rear of the first paper sheet, the front of the second paper sheet, the rear of the second paper sheet and so on. Then, an image is formed on the rear of each paper sheet only after the paper sheet carrying an image on its front has been passed through the entire duplex conveying path, resulting in the waste of time.
The interleaf control system has been proposed to enhance productivity. Specifically, the interleaf control system first prints images on the fronts of two or more consecutive paper sheets while sequentially conveying them to an intermediate path. The system again feeds the first paper sheet carrying the image thereon to a recording unit in order to print an image on the other side or rear thereof. Just after an image has been printed on the rear of the above paper sheet, the system feeds a new paper sheet from a paper feeding section to the recording unit so as to print an image on the front thereof. Thereafter, the system repeats the feed of a new paper sheet (front) from the paper feeding section and the refeed of the paper sheet carrying an image on one side thereof form the duplex copy unit alternately. In this manner, a new paper sheet is fed between two one-sided paper sheets, so that a paper sheet always exists on a conveyance path. This is successful to enhance productivity.
For example, in a two-interleaf control system, images are sequentially printed on the front of the first paper sheet, the front of the second paper sheet, the rear of the first paper sheet, the front of the third paper sheet, the rear of the second paper sheet, the front of the fourth paper sheet and so on. In a three-interleaf control system, images are sequentially printed on the front of the first paper sheet, the front of the second paper sheet, the front of the third paper sheet, the rear of the first paper sheet, the front of the fourth paper sheet, the rear of the second paper sheet and so on.
However, an image recording apparatuses using the conventional interleaf control system has some problems left unsolved, as will be described in detail later.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 7-160067 and 8-234631.
It is therefore an object of the present invention to provide a duplex image recording method capable of reducing a loss ascribable to interleaf control when dealing with the last paper sheet and thereby enhancing productivity in a duplex record mode, and an apparatus for practicing the same.
It is another object of the present invention to provide a duplex image recording method capable of effecting optimal processing (reduction of a loss at the final stage of printing) with each of a copier, a printer and so forth different in an image data reading method from each other even when only a single copy of printings is desired and thereby improving productivity, and an apparatus for practicing the same.
It is a further object of the present invention to provide a duplex image recording method capable of obviating, when a plurality of copies of duplex printings are produced from a plurality of simplex or one-sided documents by the conventional interleaf control system, not only the loss in the final stage but also a loss at the initial stage to thereby realize 100% duplex productivity (simplex image recording time=duplex image recording time), and an apparatus for practicing the same.
In accordance with the present invention, in a method of recording, among image data stored in an order of page, two consecutive pages of image data on the first and second sides of a recording medium, respectively, by interleaf control that records image data alternately on the second side of the recording medium carrying an image on the first side and a new recording medium. Assuming that the image data are continuously recorded on the first sides of n consecutive recording media at the beginning, the interleaf control continuously prints the image data on the first sides of n +1 consecutive recording media at the final stage of printing.
Also, in accordance with the present invention, a duplex image recording apparatus records images on the first and second sides of a recording medium by interleaf control that records images alternately on the second side of the recording medium carrying an image on the first side and a new recording medium. The apparatus includes a storage for storing image data in the order of page. A recording device records, among the image data stored in the storage, two consecutive pages of image data on the first and second sides of a recording medium, respectively. A reversing device reverses, after the image data has been recorded on the first side of the recording medium, the recording medium. A conveying device conveys the recording medium reversed by the reversing device toward the recording device to thereby allow the image data to be recorded on the second side of the recording medium. A controller controls the storage, recording device, reversing device, and conveying device. Assuming that the image data are continuously printed on first sides of n consecutive recording media at the beginning, the controller causes the image data to be printed on the first sides of n+1 consecutive recording media at the final stage of printing.